Question: $ { {-4} \times \left[\begin{array}{r}{2} \\ {1} \\ {3}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-4}\times{2} \\ {-4}\times{1} \\ {-4}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-8} \\ {-4} \\ {-12}\end{array}\right]}$